Atomically dispersed Ni–N4 species and Ni nanoparticles constructing N-doped porous carbon fibers for accelerating hydrogen evolution

Single-atom catalysis has aroused enormous attention due to the highly exposed active sites and nearly 100% atomic utilization. However, the relatively low metal atoms loading limits their catalytic activities. Herein, we report N-doped carbon fibers supported Ni single atoms and nanoparticles hybrid (Ni SA/NP-NCF-800) by the combined strategies comprising electrospinning, pyrolysis, and etching. The in-situ formed SiO2 and Ni particles serve as the hard templates to create highly porous architecture throughout the entire fibers, enabling the Ni species to efficiently anchor on carbon matrix to generate a high single atoms loading of 1.83 wt%, as well as provide accessible channels for mass transport and electrolyte diffusion. The unique configuration endows the hybrid with outstanding hydrogen evolution performance along with the low overpotential and robust long-term durability in 1 M KOH. The synchrotron radiation analysis and density functional theory calculations experimentally and theoretically reveal the isolated Ni was coordinated with neighboring four N atoms, which could lead to the re-arranged electron structure of Ni nanoparticles. The synergistic effect of atomically dispersed Ni and nanoparticles leads to the significantly enhanced water adsorption/dissociation abilities and optimized H adsorption free energy in alkaline media, thus paving a new avenue to design single atoms based electrocatalysts.